a. Field of Invention
This invention pertains to a IR focal plane array useful in IR imaging applications, and more particularly to arrays formed by spin casting a plastic film onto a wafer.
b. Description of the Prior Art
Accurate and reliable temperature measurements and imaging are performed using solid-state lasers and non-linear optical materials, laser transmitters, detectors and LIDAR subsystems, and infrared detectors.
Photon detectors based on technologies such as lead salts, Schottky barriers and indium antimonide are also currently available. However, these detectors require cryogenic cooling to achieve high detectivities. Furthermore, the quantum nature of the photon absorption implies not only a spectral cutoff wavelength but also a detectivity which is non-uniform with respect to wavelength.
IR thermal detectors based on thermistor bolometers, thermopiles and pyroelectric detectors have been available for several decades. However, these suffer from the drawback of lower speeds in comparison with the photon detectors.
To date, infrared imagery containing focal plane arrays of more than 80,000 "uncooled" detectors sensitive to infrared radiation in the 8 to 14 micron wavelength region have been fabricated and tested. These detectors do not require cryogenic cooling or mechanical scanning, and have demonstrated noise-equivalent temperature difference (NETD) values of 0.1.degree. C. Two different detector technologies, one ferroelectric and the other bolometric, have been used in these focal plane arrays. The uncooled sensor technology has been incorporated into prototype security sensors and weapons sights that can be used as handheld surveillance devices.
However, these detectors have been found to be unsatisfactory. Uncooled focal plane array technologies, based on ferroelectrics, suffer from the requirement of bump-bonding to a silicon readout circuit. Bump-bonding is a technique where the readout electronics of the m*n array and the detector array are two separate entities which are bonded together physically by an interfacing material, typical indium, which is the shape of bumps or mounds on each of the m*n detector pixels and corresponding readout electronics. The detector array and the readout chip are aligned and the bump bonds formed by heat or pressure until the array and readout chips are fused together. The bump-bonding approach is further plagued by producibility problems such as mechanical damage to the detector due to the cold weld process, alignment and surface oxidation. Reticulated lithium tantalate pyroelectric arrays have also been used to fabricate uncooled focal plane arrays but also suffer from the requirement of bump-bonding.
Moreover, the detectors used in bump technology require reticulation of the pixel elements in order to reduce the thermal crosstalk, which otherwise is quite significant and causes deterioration of the modulation transfer function (MTF).